[tip:timers/core] posix_cpu_timer: Check thread timers only when there are active thread timers

tip-bot for Jason Low
2015-10-15T09:29:09Z

Commit-ID: 934715a191e4be0c602d39455a7a74316f274d60
Gitweb: http://git.kernel.org/tip/934715a191e4be0c602d39455a7a74316f274d60
Author: Jason Low <jason.low2@hp.com>
AuthorDate: Wed, 14 Oct 2015 12:07:54 -0700
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 15 Oct 2015 11:23:41 +0200

posix_cpu_timer: Check thread timers only when there are active thread timers

The fastpath_timer_check() contains logic to check for if any timers
are set by checking if !task_cputime_zero(). Similarly, we can do this
before calling check_thread_timers(). In the case where there
are only process-wide timers, this will skip all of the computations for
per-thread timers when there are no per-thread timers.

As suggested by George, we can put the task_cputime_zero() check in
check_thread_timers(), since that is more of an optization to the
function. Similarly, we move the existing check of cputimer->running
to check_process_timers().

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: George Spelvin <linux@horizon.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: hideaki.kimura@hpe.com
Cc: terry.rudd@hpe.com
Cc: scott.norton@hpe.com
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1444849677-29330-3-git-send-email-jason.low2@hp.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/posix-cpu-timers.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index aa4b6f4..6f6e252 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -864,6 +864,13 @@ static void check_thread_timers(struct task_struct *tsk,
unsigned long long expires;
unsigned long soft;

+ /*
+ * If cputime_expires is zero, then there are no active
+ * per thread CPU timers.
+ */
+ if (task_cputime_zero(&tsk->cputime_expires))
+ return;
+
expires = check_timers_list(timers, firing, prof_ticks(tsk));
tsk_expires->prof_exp = expires_to_cputime(expires);

@@ -962,6 +969,13 @@ static void check_process_timers(struct task_struct *tsk,
unsigned long soft;

/*
+ * If cputimer is not running, then there are no active
+ * process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
+ */
+ if (!READ_ONCE(tsk->signal->cputimer.running))
+ return;
+
+ /*
* Collect the current process totals.
*/
thread_group_cputimer(tsk, &cputime);
@@ -1169,12 +1183,8 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* put them on the firing list.
*/
check_thread_timers(tsk, &firing);
- /*
- * If there are any active process wide timers (POSIX 1.b, itimers,
- * RLIMIT_CPU) cputimer must be running.
- */
- if (READ_ONCE(tsk->signal->cputimer.running))
- check_process_timers(tsk, &firing);
+
+ check_process_timers(tsk, &firing);

/*
* We must release these locks before taking any timer's lock.